Peelable PTFE sheaths and methods for manufacture of same

ABSTRACT

The present invention provides improved medical introducer devices which incorporate a single or multi-layer PTFE peelable sheath. Devices of the present invention are suitable for use in inserting an ancilliary medical device, e.g., a catheter, guide wire and the like, into a patient. Methods of the present invention also are disclosed which employ a precision sintering process in order to produce sheaths having excellent tear properties and optimal peelability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to single and multi-layerpolytetrafluoroethylene (PTFE) peelable sheaths and methods formanufacturing and use of such sheaths. Sheaths of the present inventionare particularly suited for use as cannulas and other medical introducerdevices.

2. Background

Splittable cannulas have been employed in various medical and surgicalprocedures for inserting catheters, guide wires and the like intopatients. A typical procedure provides for insertion of a dilator orneedle into the vasculature of a patient while encased within asplittable sheath. After insertion, the dilator or needle may be removedleaving the sheath protruding from the patient's vein. An ancillarymedical device, e.g., a diagnostic or therapeutic catheter or guidewire,is then threaded through the sheath into the patient. The encasingsheath is then longitudinally sheared and removed from the catheter orguide wire and the patient such as by applying opposing force to opposedwings or tabs of the introducer device. See e.g., U.S. Pat. Nos.5,334,157; 5,221,263; 5,141,497; 5,098,392; 4,772,266; and 4,243,050;and WO 97/14456 and WO 97/14468.

For ease in shearing and overall handling of the device, it is desirableto employ a sheath of minimal thickness, e.g., thin-walled, having somedegree of flexibility.

Notable disadvantages have been observed when using devices whichincorporate a “tear-away” or splittable sheath. For example, easy andnon-traumatic removal of the sheath is critical. It is possible that thesheath may not tear evenly or completely, thereby necessitatingadditional maneuvering and application of excessive force to the device.Excessive movement or force exerted upon the sheath is likely to causedamage to the vasculature of the patient. There is also the potential ofaccidentally dislodging the catheter from its inserted position whiletrying to remove the sheath.

Many design configurations and processes have been investigated in aneffort to overcome the various deficiencies observed in devices of theprior art which incorporate a peelable sheath.

For example, certain devices and methods were developed which employed askiving process in order to produce peelable sheaths. Using such aprocess, approximately one half of the wall thickness of the tubingmaterial, e.g. a plastic, typically is cut away in a longitudinaldirection. In that way, a weak spot in the tubing wall is presentedwhere the tubing material can be peeled.

U.S. Patent No. 4,306,562 (Cook) discloses a flexible, tear apartcannula which may be removed by pulling tabs on opposite sides of thecannula following insertion of a catheter or other device into the body.That patent reports that the cannula tears readily in a longitudinaldirection along the length of the structure because it comprisesmaterial having a longitudinal orientation, e.g.,polytetrafluoroethylene or other plastics. The longitudinal orientationis achieved using a standard extrusion process, and a slitting operationis used to create the tabs for pulling the cannula apart. See also U.S.Pat. No. 4,581,025 (Cook).

It has been shown, however, that the cannulas produced in accordancewith the Cook patents present certain limitations. For example, despitethe fact that the tubing material has a longitudinal orientation,peelability still can be problematic. Additionally, certain additiveswhich are added to the preferred tubing material, TEFLON (TEFLON is aregistered trademark of DuPont for polytetrafluoroethylene), for X-rayvisualization cause discoloration when the sheath is tipped byconventional thermal processes. Thus, the Cook devices may only beproduced in dark colors (e.g., gray and black) that hide suchdiscoloration.

U.S. Pat. No. 5,318,542 describes another process for producing a splitcannula device having predetermined break lines which reportedlyprovides enhanced disassembly of the cannula. Predetermined break linesare produced by a non-metal-cutting shaping process, thereby enhancinguniformity of the predetermined break lines and reducing the forceneeded to disassemble the cannula. See also, U.S. Pat. No. 5,104,388.

SUMMARY OF THE INVENTION

There remains a need for improved medical introducer devices whichincorporate a peelable sheath to facilitate smooth entry of an ancillarymedical device into a patient, and easy and non-traumatic removal of thesheath following insertion of the ancilliary medical device.

It would be desirable to develop a multi-layer sheath configuration,e.g., an inner layer which permits visualization by X-ray orfluoroscopic procedures, and an outer layer that is resistant todiscoloration by thermal processes. Such a configuration would bedesirable in that the device could be produced in a variety of colorsincluding white, blue or any other thermally stable color.

It also would be highly desirable to develop methods for the manufacturewhich produce single and multi-layer peelable sheaths with superior tearproperties. More specifically, it would be highly desirable to developmethods for the manufacture of such sheaths which do not rely onmechanical skiving of the sheaths. We have found that skiving does notalways produce tubing with good peel properties, especially when usingtubing materials such as polytetrafluoroethylene.

We have now produced medical introducer devices which incorporate asingle or multi-layer polytetrafluoroethylenepeelable (PTFE) sheath.

Preferred sheaths of the invention are characterized in part by beingreadily splittable along their length (longitudinally) without use ofany type of mechanical skiving, score lines or the like.

The invention is based in part on the discovery that by imparting anappropriate longitudinal peel strength to a PTFE sheath, the sheath canbe readily split as desired without the need for any type of mechanicalskiving along the sheath length. Preferred peel strengths to providesuch longitudinal splitting are disclosed below.

An appropriate peel strength is suitably imparted to a sheath by acontrolled curing process, sometimes referred to herein as “precisionsintering”. Thus, temperature and cure times are selected to provide theappropriate peel strength. Optimal temperature and cure conditions willvary among specific cure systems. That is, cure conditions may vary withthe type of heat source (e.g. radiant or convective heating), residenceor exposure times of the PTFE sheath material to the heat source(s),size (e.g. French) of the sheath material being cured, and the like. Seethe examples which follow for exemplary suitable cure conditions for thedescribed systems. Suitable cure conditions for any particular heatingsystem and sheath material also can be readily determined empirically,i.e. a sheath material can be exposed to alternative cure conditionsuntil conditions are identified that provide a desired peel strength. Inother words, cure conditions can be applied, and the peel strength ofthe cured strength measured to determine if those conditions did in factprovide a targeted peel strength value. If the peel strength is notappropriate, the cure conditions are simply varied until a desired peelstrength is provided.

Sheaths of the invention are useful for medical device applications,particularly for use in inserting an ancilliary medical device, e.g., acatheter, guide wire and the like, into a patient.

PTFE sheaths of the invention suitably may be of single layer ormultiple layer constructions.

Preferred multi-layer devices afford significant advantages over thedevices of the prior art. In one preferred multi-layer sheath of theinvention, the outer layer comprises a thermally stable, colored pigmentwhile at least one of the inner layers of the sheath comprises adetectable component, e.g. a radiopaque material for externalvisualization by X-ray or fluoroscopic procedures.

Using such a multi-layer configuration, no discoloration of the sheathis observed following conventional thermal tipping processes. Thus,devices of the present invention may be produced in a variety of colors,e.g., white, blue or any other thermally stable color, withoutsacrificing the radiopaque feature of the device.

The present invention also provides methods for manufacturing single ormulti-layer peelable sheaths for use as cannulas and other medicalintroducer devices. Methods of the present invention incorporateextrusion followed by a precision sintering process as generallydiscussed above in order to achieve optimally cured tubing for use as apeelable sheath. Thus, there is no need to mechanically skive the wallof the tubing to present a weakened, predetermined break line.

Preferred methods for single layer sheath manufacture include: providinga preform PTFE material; extruding the PTFE material into tubing usingconventional extrusion procedures; drying the tubing; and imparting adesired peel strength to the sheath that enables facile longitudinalsplitting of the sheath without any type of mechanical skiving of thesheath. Precision sintering cure conditions are suitably employed toimpart a desired peel strength. A detectable material may be added tothe preform PTFE material in an amount sufficient to facilitate externalvisualization. Preferably, the detectable material comprises aradiopaque material for visualization by X-ray or fluoroscopicprocedures.

Preferred methods for multiple layer sheath manufacture include thefollowing: providing a first PTFE material blend for forming the innerlayer of the sheath; preparing a second PTFE material for forming theouter layer of the sheath; combining the first and second PTFE materialsblends into a two layer preform; extruding the two layer preform intotubing using conventional extrusion procedures; drying the tubing; andimparting a desired peel strength to the sheath that enables facilelongitudinal splitting of the sheath without any type of mechanicalskiving of the sheath. Precision sintering cure conditions are suitablyemployed to impart a desired peel strength.

A number of inner layer preform materials may be provided depending uponthe number of inner layers desired, i.e. the multiple layer sheath mayhave 2 or more layers, typically 2, 3, 4 or 5 total layers. Again, adetectable material may be added to one of the preform materials in anamount sufficient to facilitate external visualization. Preferably, thedetectable material comprises a radiopaque material for visualization byX-ray or fluoroscopic procedures.

Additionally, different colored pigments may be added to each of theouter and inner layer preform blends. In that way, though inseparable,the layers may be visibly distinguished.

A hub unit is preferably attached to either the single layer or multiplelayer sheath on the sheath proximal end to facilitates splitting of thesheath upon application of an effective shearing force thereon. Forexample, preferred hub may have opposed outwardly extending “wing”portions that can be manipulated (e.g. downward or inward pressure) tofacilitate longitudinal splitting of the sheath.

The sheath is also preferably tipped at the distal end thereof, e.g.,using conventional thermal tipping processes.

Methods of introducing an ancilliary medical device, e.g., catheter orguidewire, using a device of the present invention generally include:inserting a needle or dilator assembly into the bore of a peelablesheath constructed in accordance with the present invention; piercingand dilating the vasculature of the patient using such an assembly;withdrawing the needle or dilator assembly from the sheath component ofthe device; inserting the catheter or guide wire through the bore of thesheath to the desired target location; applying outwardly cooperatingforces to the hub unit, e.g., via attached wing portions, to axiallyshear the sheath; and removing the sheath from the vasculature of thepatient.

Using methods of the present invention, single or multi-layer peelablesheaths are provided that facilitate easy, non-traumatic removal of thesheath following insertion of the ancilliary medical device.

Other aspects of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a medical introducer device which incorporatesa single layer peelable sheath in a preferred embodiment of the presentinvention.

FIG. 2 is a side view of a medical introducer device which incorporatesa multi-layer peelable sheath in an alternate preferred embodiment ofthe present invention.

DETAILED DESCRIPTION

As discussed above, the present invention provides single andmulti-layer peelable sheaths for use in medical devices such as cannulasand other introducer devices. Introducer devices are routinely used in avariety of medical and surgical applications, e.g., for insertion of anancilliary medical device such as a catheter, guide wire into a patient.The present invention employs a precision sintering process in order toproduce sheaths having excellent tear properties and optimalpeelability.

Preferred sheaths of the invention will exhibit a peel strength of atleast about 0.6 lbs., more preferably at least about 0.70 lbs., stillmore preferably at least about 0.80 lbs., 1.0 lbs., 1.2 lbs., 1.4 lbs.,1.6 lbs., 1.8 lbs. or 2.0 lbs., with a maximum peel strength of about2.8 or 3.0 lbs.

Further preferred is where the sheath exhibits a relatively narrowstandard deviation around a tested peel strength, such a standarddeviation of no more than about ±0.40 lbs of a specific value, morepreferably a standard deviation of no more than about ±0.30 lbs, 0.20lbs or 0.10 lbs of a specific tested value.

As discussed above, preferred peel strengths will vary with sheath size,with generally higher peel strengths preferred for larger sheaths. Moreparticularly, for a sheath having a size up to about 9 French (typicallyabout 2, 3, or 4 French up to about 8 or 8.5 French), preferred peelstrengths will be from about 0.5 lbs. up to about 2.0 lbs., morepreferably 0.6 lbs to about 2.0 lbs. For a sheath having a size fromabout 9 to about 13 French, preferred peel strengths will be from about0.75 lbs. up to about 2.5 lbs., more preferably 1.0 lbs to about 2.0lbs. For a sheath having a size from about 14 to about 18 French orgreater, preferred peel strengths will be from about 1.0 lbs. up toabout 3.0 lbs., more preferably 1.0 lbs to about 2.5 lbs.

Referring now to the Drawings, FIG. 1 shows a preferred embodiment of amedical introducer device 10 constructed in accordance with the methodsof the present invention. Device 10 comprises a single layer, peelablesheath 11 having a proximal end 12 and a tapered distal end 12′, and abore 13 extending therebetween. (In accordance with conventionalpractice, “proximal end” designates herein the specified end closest tothe medical personnel manipulating the introducer device, and “distalend” designates the specified end closest to the patient.)

Sheath 11 is formed from a polytetrafluoroethylene polymer (e.g.,TEFLON, registered trademark for polytetrafluoroethylene, commerciallyavailable from DuPont). Sheath 11 may further comprise materials such asfillers, colorants, and the like. Typical additional additives to thePTFE will be inorganic materials. It also will be possible, althoughtypically less preferred, to include additional organic materials,particularly high Tg polymers, with the PTFE.

As discussed above, sheath 11 preferably further comprises a detectablematerial, e.g., a radiopaque material, in an amount sufficient forexternal visualization by X-ray or fluoroscopic procedures. Preferredradiopaque materials include barium sulfate, tungsten, bismuthsub-carbonate and bismuth trioxide. Preferably, the amount of radiopaquematerial present in the inner layer ranges from about 1% or 2% to about12% by weight. Such a configuration permits visualization of the sheathwithin a patient by X-ray or fluoroscopic procedures.

Referring now to FIG. 2, an alternate embodiment of a medical introducerdevice of the present invention is shown. Device 20, constructed inaccordance with the methods of the present invention, is shown toinclude a multi-layer, peelable sheath 23 having a proximal end 24 and atapered distal end 24′, and a bore 25 extending therebetween.

Sheath 23 preferably includes a thermally stable outer layer 26 and atleast one inner layer 27. Preferably, both of these layers are formedfrom a flexible polymeric material, preferably a polytetrafluoroethylenepolymer (e.g., TEFLON, registered trademark for polytetrafluoroethylene,commercially available from DuPont).

In preferred embodiments of the present invention, outer layer 26further comprises a pigment that is not discolored by thermal processes.

In preferred embodiments of the present invention, inner layer 27further comprises a detectable material, e.g., a radiopaque material, inan amount sufficient for external visualization by X-ray or fluoroscopicprocedures. Preferred radiopaque materials include barium sulfate,tungsten, bismuth sub-carbonate and bismuth trioxide. Preferably, theamount of radiopaque material present in the inner layer ranges fromabout 1 or 2% to about 12% by weight. Such a configuration permitsvisualization of the sheath within a patient by X-ray or fluoroscopicprocedures.

In particularly preferred embodiments, inner layer 27 additionallycomprises a pigment (e.g., different in color from that of the outerlayer) for visual distinction from outer layer 26.

Referring now to both FIGS. 1 and 2, devices of the present inventionpreferably further comprise a hub unit 14 attached, e.g., molded, to thesheath at a proximal end thereof. The hub unit 14 is capable ofsplitting the sheath upon application of an effective shearing forcethereon.

Preferably, hub unit 14 is formed of polypropylene or other suitablematerial. In preferred embodiments, hub unit 14 substantiallycircumscribes the proximal end of the respective sheath and comprises alongitudinal score or indentation 15 on opposing sides. In that way, thehub is in contact with a significant circumferential surface area at theproximal end of the respective sheaths and a defined break line ispresented for easy tearing of the sheath, e.g., along a longitudinalarea 16. Using such a configuration, the potential for the sheath totear unevenly or incompletely is avoided or at least significantlyreduced.

In preferred embodiments of the present invention, two or more wingportions 17 and 18 are attached, e.g., molded to the hub unit 14. Wingportions 17 and 18 preferably extend outwardly from the hub unit insubstantially diametrically opposed positions. Wing portions 17 and 18facilitate easy grasping with respect to hub unit 14 and effectiveshearing of sheath 11 and sheath 23.

It also is particularly preferred that the outer surfaces of wingportions 17 and 18 include topography to aid in manipulation and overallhandling of the introducer device. For example, as shown in theillustrative embodiments of FIGS. 1 and 2, preferably the exposed sidesof wing portions 17 and 18 have a plurality of raised gripping surfaces19.

In particularly preferred embodiments of the present invention, raisedgripping surfaces 19 or other area(s) of wing portions 17 and 18 arecolor-coded to designate particular sheath dimensions. This featureenables easy identification by attendant medical personnel of a desiredsheath size.

Sheaths 11 and 23 are typically adapted to snugly receive a conventionaldilator assembly 20 or alternately, a needle assembly (not shown) inorder to facilitate entry into a vein or artery of a patient.

Accordingly, in preferred embodiments of the present invention, wingportion 17 further comprises a locking lip 21 which secures flange 22 ofdilator assembly 20 or a comparable flange of a needle assembly.

Generally, distal end 28 of dilator assembly 20 extends beyond thetapered distal end of the sheath in order to minimize trauma to thevasculature of the patient during the procedure.

Preferably, dilator assembly 20 is formed from a fluorinatedethylene-propylene resin. Other preferred fluorinated resins include,e.g., a tetrafluoroethylene polymer such as TEFLON (registered trademarkof DuPont for polytetrafluoroethylene).

Following dilation of the vasculature of the patient, dilator assembly20 is withdrawn and replaced with the desired ancilliary medical device,e.g. catheter or guidewire. Upon application of force to the hub unit 14via wing portions 17 and 18, the sheath is peeled along longitudinaltear line 16 leaving only the ancilliary medical device in place withinthe vasculature of the patient.

Suitable dimensions of the components of devices of the presentinvention can vary rather widely depending on the intended applicationand such dimensions can be readily determined by those skilled in theart based on the present disclosure.

Generally, dilator assembly 20 (or, alternately, a needle assembly)should have a diameter suitable for insertion into the selectedvasculature of a patient. Sheath 11 and sheath 23 should have a diametersufficient to accommodate such an assembly, and subsequently a catheter,guide wire or the like. Also, the diameters of the dilator as well asthe sheath for circumscribing the dilator will be greater than thecorresponding diameters of a device that employs a percutaneous needlerather than a dilator assembly.

For example, in particularly preferred embodiments of the presentinvention, peelable sheath 11 is about 5 to about 6 inches in length,denoted as x in FIG. 1. Preferably, dilator assembly 20 has a useablelength (length excluding luer threads or other connector at proximal end28) from about 7 inches to about 8 inches, denoted as y in FIG. 1.

Comparable dimensions, denoted by x′ and y′ in FIG. 2, are suitablypreferred for the multi-layer embodiment 20.

Other preferred dimensions for devices of the present invention areshown in Table 1 below.

TABLE 1 DILATOR SHEATH O.D. TIP I.D. O.D. AVG. MIN. AVG. FRENCH (%/&(+.002/ (%/& I.D. SIZE .001) −.000) .001) MIN WALL  4F .052 .027 .076.054 .008/.009  5F .066 .037 .090 .068 .008/.009  6F .079 .037 .103 .081.008/.009  7F .092 .040 .118 .094 .009/.010  8F .105 .040 .131 .107.009/.010  9F .118 .040 .144 .120 .009/.010 10F .131 .040 .159 .133.010/.011 10.5F .137 .040 .165 .139 .010/.011 11F .144 .040 .172 .146.010/.011 12F .157 .040 .185 .159 .010/.011 12.5F .162 .040 .192 .164.011/.012 13F .170 .040 .200 .172 .011/.012 14F .184 .040 .214 .186.011/.012 15F .196 .040 .227 .198 .011/.012 16F .210 .040 .240 .212.011/.012 18F .236 .040 .266 .238 .011/.012

The present invention also provides methods of manufacturing single ormulti-layer peelable sheaths for use in medical devices such as cannulasand other introducer devices, e.g., sheaths for insertion of a catheter,guide wire and the like into a patient. Methods of the present inventionincorporate extrusion followed by a precision sintering process in orderto achieve optimally cured tubing for use as a peelable sheath. Thus,there is no need to mechanically skive the wall of the tubing to presenta weakened, predetermined break line.

In the case of the multi-layer peelable sheath, methods of the presentinvention preferably also comprise adding different colored pigments toeach of the outer and inner layer preform blends. Generally, suchpigments are added in amounts which are sufficient to produce thedesired colors. In that way, though inseparable, the layers may bevisibly distinguished.

The multi-layer configuration presents significant advantages withrespect to the devices of the prior art. In particular, we havediscovered that if the sheath consists of a co-extrusion (two or morelayers), it is possible to make any color sheath and that there is novisible discoloration of the external layer after thermal tipping. Thus,there is no need for devices of the present invention to be limited to anarrow range of colors (e.g., to dark colors only). Further, the abilityto produce sheaths in lighter colors has the added advantage of enablingone to visualize contaminants that may be present in the sheath.

Preferably, a hydrocarbon lubricant is added to the preform blends, andthe preform blends are allowed to equilibrate for a period of severalhours prior to their combination in the case of the multi-layer sheathor prior to extrusion in the case of the single layer sheath.

Sheaths of the present invention are produced using standard single ormulti-layer polytetrafluoroethylene (PTFE) extrusion procedures. Forexample, the two layer PTFE extrusion process is typically used to makefuel tubes with carbon-filled PTFE on the inside and natural PTFE on theoutside. In utilizing this process, the present invention presents animprovement in terms of thermal resistance and color integrity oftubing.

As noted above, curing of the tubing is performed using a precisionsintering process, e.g., reduced sintering. We have discovered thatreduced sintering provides single or multi-layer tubing with excellenttear properties and optimal peelability. In contrast to the prior art,using the methods of the present invention, no skiving of the tubing isnecessary to produce a peelable sheath.

Using the precision sintering process, the tubing is run through aseries of temperature adjusted sintering ovens in order to producetubing which is not only cured to the desired degree but which also hasoptimal tear properties, e.g., tensile strength and elongation, as wellas peel strength.

Typically, the peel strength and other properties of the tubing aremanually monitored at various intervals during the reduced sinteringprocess. Various temperature adjustments and sintering times may beemployed in order to produce tubing having the desired properties.However, the tubing is cured only until the desired peel strength isobtained.

Optimal peel strength will vary with tubing size. Referring to Table 2below, target peel values are shown for various tubing sizes.

TABLE 2 FRENCH PEEL STANDARD SIZE VALUE DEVIATION   4 F-8.5 F 0.85+/−0.50 lbs.  9 F-13 F 1.25 +/−0.50 lbs. 14 F-18 F 1.80 +/−0.60 lbs.

In preferred embodiments of the present invention, methods ofmanufacture further comprise attaching, e.g., molding, a hub unit ontothe proximal end of the sheath which facilitates splitting of the sheathupon application of an effective shearing force thereon; attaching and aplurality of wing portions to opposing sides of the hub unit; andtipping the sheath at a distal end thereof, e.g., using conventionalthermal tipping processes.

The present invention also provides methods of introducing an ancilliarymedical device, e.g., catheter or guidewire, using a device of thepresent invention. Such methods generally include: inserting a needle ordilator assembly into a peelable sheath constructed in accordance withmethods of the present invention; piercing and dilating the vasculatureof the patient using such an assembly; withdrawing the needle or dilatorassembly from the sheath component of the device; inserting the catheteror guide wire through the bore of the sheath to the desired targetlocation; applying outwardly cooperating forces to the hub unit, e.g.,via attached wing portions, to axially shear the sheath; and removingthe sheath from the vasculature of the patient.

The following non-limiting examples are illustrative of the invention.

EXAMPLE 1

25 lb. of PTFE fine powder (Teflon® 6C, DuPont) was mixed with 4.35 lb.of a hydrocarbon lubricant (Isopar® G, Exxon), 3.245 lb. of aradioopaque filler (67% Bi2O3 in Isopar G), 0.5 lb. of Gray pigmentconcentrate (67% gray pigment in Isopar G) and 0.25 lb. of black pigmentconcentrate (67% black pigment in Isopar® G). (Final composition is 7.8%Bi₂O₃, 1.2% gray, 0.6% black, based on total solids) These ingredientswere mixed in a Patterson-Kelly V-cone blender for 20 minutes. This mixwas then allowed to age for several hours to equilibrate.

The blend was made into a preform (2.5″ OD, 0.625″ ID). The object ofpreforming is to compact the blends in size and to make a preform thatcan be inserted into an extrusion machine. The preform was placed intoan extrusion machine and extruded into tubing using a die and mandril(0.2880″ OD, 0.2650″ ID). The tubing was run through a drying oven toremove the hydrocarbon lubricant. The tubing was then run through 3sintering ovens to cure the material. This tubing was then cut into8.25″ lengths.

The tubing produced had dimensions of 0.240″ OD×0.2170″ ID×8.25″ long.The wall thickness was 0.011 5″. The overall tube was black with a shinysurface.

Referring to Table 3 below, properties of the tubing produced in thisexample are shown below as “Sample 2”. Data for Samples 1, 3 and 4 areshown for purposes of comparison.

TABLE 3 SAMPLE SAMPLE 1 2 SAMPLE SAMPLE PRIOR PRESENT 3 4 ART INVENT-UNDER- OVER- SAMPLE ION CURE CURE Drying oven 1 (° F.) 400 400 400 400Curing oven 1 (° F.) 840 720 700 1000 Curing oven 2 (° F.) 940 820 8001080 Curing oven 3 (° F.) 1040 920 900 1180 Melting Point (° C.) 326.63326.57 343.77 326.03 Width at Half 4.0 6.0 5.6 3.3 Height (° C.) TensileStrength 7083 6817 1333 5417 (PSI) Elongation (%) 288 309 233 351 Peelstrength (lb) 1.95 1.56 1.2 2.67 Peel Comments Uneven Straight,Straight, Uneven peel, even even peel. peel, partial peel Lots ofpartial peel strangers. peel

Description of Samples:

Sample 1—This sample is presented for purposes of comparison. It is acommercially available product comprising PTFE, and has a narrow meltingpoint peak at 327 degrees C. When split and peeled, it requires higherpeel force and does not peel smoothly. The tubing begins to peel andthen one of the sections begins to narrow down and eventually endsbefore all of the tubing is split (partial peel).

Sample 2—This sample corresponds to a peelable product manufactured inaccordance with the methods of present invention. This product is notfully cured as indicated by the wider melting point peak. The tensilestrength and elongation are similar to the fully cured product. However,the peel strength is reduced by 20% in relation to the fully curedproduct. The peel is straight and even so that the entire tubing issplit.

Sample 3—This sample corresponds to a product that is almost completelyuncured. This is visible by a melting peak at 344 degrees C. versus 327degrees C. for the other samples. This product is mottled white andblack due to the undercure. The peel is straight and even, however,there are significant numbers of fibers that extend from the peeledsurface after peeling. This is unacceptable to the end user since apiece may tear away and contaminate the area. In addition, the physicalproperties are significantly reduced due to the lack of curing of theproduct.

Sample 4—This sample corresponds to a product that is cured harder thannormal. This overcure is visible by the melting peak half width. Thisproduct does not peel straight, similar to the fully cured product.

EXAMPLE 2

Blend 1—55.1 lb. of PTFE fine powder (Teflon® 6C, DuPont) was mixed with9.048 lb. of a hydrocarbon lubricant (Isoparg G, Exxon), and 7.151 lb.of a radiopaque filler (67% Bi2O3 in Isopar G) (final composition is6.7% Bi₂O₃ based on total solids). These ingredients were mixed in aPatterson-Kelly V-cone blender for 20 minutes. This mix was then allowedto age for several hours to equilibrate.

Blend 2—55.1 lb. of PTFE fine powder (Teflon® 6C, DuPont) was mixed with10.379 lb. of a hydrocarbon lubricant (Isoparu G, Exxon), and .573 lb.of a white pigment filler (67% white pigment in Isopar G). Theseingredients were mixed in a Patterson-Kelly V-cone blender for 20minutes. This mix was then allowed to age for several hours toequilibrate.

The blends were made into a two layer preform (2.5″ OD, 0.625″ ID) withBlend 1 on the ID and Blend 2 on the OD. The object of preforming is tocompact the blends in size and to make a preform that can be insertedinto an extrusion machine. The preform was placed into an extrusionmachine and extruded into tubing using a die and mandril. (0.2880″OD,0.2650″ID) The tubing was run through a drying oven to remove thehydrocarbon lubricant. The tubing was then run through 3 sintering ovensto cure the material. This tubing was then cut into 8.25″ lengths.

The tubing produced has dimensions of 0. 240″ OD×0.2170″ ID×8.25″ long.The wall thickness is 0.011 5″. The overall tube is two layers with ashiny white outside layer and a yellow inside layer.

TABLE 4 SAMPLE 1 PRESENT SAMPLE 2 SAMPLE 3 INVENTION UNDERCURE OVERCUREDrying oven 1 (° F.) 400 400 400 Curing oven 1 (° F.) 820 720 1000Curing oven 2 (° F.) 920 820 1160 Curing oven 3 (° F.) 1000 920 1160Melting Point (° C.) 325.96 343.33 329.38 Tensile Strength (PSI) 70001333 7400 Elongation (%) 250 250 350 Peel strength (lb) 1.56 0.4 >2.5*Peel Comments Straight, Straight, *Could even peel even peel. not peel.Lots of stringers.

Description of Samples:

Sample 1—This is an example of the present invention. This is a peelableproduct. This product is precision sintered. The peel strength istypical for precision sintered product. The peel is straight and even sothat the entire tubing is split.

Sample 2—This sample is almost completely uncured product. This isvisible by a melting peak at 344 degrees C. versus 327 degrees C. forthe other samples. This product is opaque, dull white due to theundercure. The peel is straight and even, however, there are significantnumbers of fibers that stick out of the peeled surface after beingpeeled. The peel strength is unacceptably low. This is unacceptable tothe end user since a piece may tear away and contaminate the area. Inaddition, the physical properties are significantly reduced due to thelack of curing of the product.

Sample 3—This product is fully cured. This makes a tube that isdimensionally stable, but cannot be peeled. The peel force increases togreater than 2.5 lb. and then the product tears. This product does notpeel evenly.

EXAMPLE 3

Tubing manufacturing: Blend 1-25 lb. of PTFE fine powder (Teflon® T6C,DuPont) was mixed with 4.5 lb. of a hydrocarbon lubricant (Isopar® G,Exxon) and 3.3 lb. of a radiopaque filler (67% Bi₂O₃ in Isopar G,Caloric) in a Patterson-Kelly V-cone blender. The materials were blendedfor 20 minutes. This mix was then allowed to age for several hours toequilibrate.

Blend 2-25 lb. of PTFE fine powder (Teflon® T6C, DuPont) was mixed with5.1 lb. of a hydrocarbon lubricant (Isopar® G, Exxon) and 0.3 lb. of awhite pigment (67% white pigment in Isopar G, Caloric) in aPatterson-Kelly V-cone blender. The materials were blended for 20minutes. This mix was then allowed to age for several hours toequilibrate.

The two blends were then made into a two layer preform (2.5″ OD, 0.625″ID) with Blend 2 on the OD and Blend 1 on the ID. (The object ofpreforming is to compact the blends in size and to make a preform thatcan be inserted into an extrusion machine.) The preform was placed intoan extrusion machine and extruded into tubing. The tubing was runthrough a drying oven at approximately 400 degrees F. to remove thehydrocarbon lubricant. The tubing was then run through sintering ovensat approximately 1000 degrees F. to cure the material. This tubing wascut into 8.25″ lengths.

The tubing produced had dimensions of 0.144″ OD×0.125″ ID×8.25″ inlength with a wall thickness of 0.0095″. The outer 0.00475″ was Blend 2and the inner 0.00475″ was Blend 1. The overall tube had a white colorwith a yellow inside when cut apart.

Device manufacture: The tubing was then punched with two holes. A slitwas made between the two holes. Buttons were placed in the punched holesand a hub was overmolded onto the tubing. The opposite end was thentipped using a Rf tipping machine and trimmed to size. The finishedsheath assembly was white in color with no visible discoloration. Thesheath assembly was then placed over a matching size dilator.

EXAMPLE 4

This example shows how additional heat added to a precision sinteredproduct renders it useless for peelable PTFE. The table illustrates thatprecision sintered product can be taken out of the useful range by theapplication of additional heat. It also shows that skived product is notaffected by the addition of additional heat.

TABLE 5 SAMPLE 1 SAMPLE 2 SAMPLE 3 Skived No No Yes Precision sinteredYes Yes Yes Post cured No Yes Yes Peel Strength (lb.) 1.63 2.93 1.26Peel Comments Straight, even peel Uneven peel, Straight even peelpartial peel

Description of Samples:

Sample 1—Product from Example 1, Sample 2.

Sample 2—Product from Example 1, Sample 2 was taken and placed in a 700degree F. oven for 20 minutes. This product is no longer precisionsintered since it was post-sintered.

Sample 3—Product from Example 1, Sample 2 that was skived and thenplaced in a 700 degree F. oven for 20 minutes. This product is no longerprecision sintered since it was post-sintered.

COMPARATIVE EXAMPLE 1

The tubing was made identical to Example 3 except that instead of usingBlend 2 on the OD, Blend 1 was used for the entire preform. Thus, onelayer of tubing is produced that is Blend 1 throughout. This producedtubing that was yellow in color.

The tubing was finished in the same manner as listed in Example 3. Thefinished sheath assembly was yellow in color with brown and blackcolored spots in the tipped section. This is unacceptable for highquality product.

COMPARATIVE EXAMPLE 2

Blend 3 is a combination of Blend 1 and Blend 2-25 lb. of PTFE finepowder (Teflon® T6C, DuPont) was mixed with 4.4 lb. of a hydrocarbonlubricant (Isoparg G, Exxon), 3.3 lb. of a radiopaque filler (67% Bi₂O₃in Isopar G, Caloric), and 0.3 lb. of a white pigment (67% white pigmentin Isopar G, Caloric) in a Patterson-Kelly V-cone blender. The materialswere blended for 20 minutes. This mix was then allowed to age forseveral hours to equilibrate.

The tubing was made identical as that described in Comparative Example 1except that instead of using Blend 2, Blend 3 was used. This producedtubing that was white in color and radiopaque.

The tubing was finished in the same manner as described in Example 3.The finished sheath assembly was white in color with brown and blackcolored spots in the tipped section. This is unacceptable for highquality product.

The foregoing description of the present invention is merelyillustrative thereof, and it is understood that variations andmodification can be made without departing from the spirit or scope ofthe invention as set forth in the following examples and claims.

What is claimed is:
 1. A medical introducer device comprising: (a) amulti-layer, peelable PTFE sheath having a bore extending therethrough,and that does not include mechanically produced skiving for longitudinalsplitting of the sheath, the sheath thermally cured to provide a peelstrength of at least about 0.5 lbs with a standard deviation of nogreater than about 0.40; and (b) a hub unit attached at a proximal endof the peelable sheath which facilitates splitting of the peelablesheath upon application of an effective shearing force thereon.
 2. Thedevice of claim 1 wherein the sheath has a peel strength of at leastabout 0.70.
 3. The device of claim 1 wherein the sheath has a peelstrength of at least about 1.0.
 4. The device of claim 1 wherein thesheath has a peel strength standard deviation of no more than about0.30.
 5. The device of claim 1 wherein the sheath has a peel strengthstandard deviation of no more than about 0.20.
 6. The device of claim 1further comprising a plurality of wing portions attached to the hub uniton opposing sides for grasping the hub unit.
 7. The device of claim 1further comprising a needle or dilator assembly extending longitudinallywithin the bore of the peelable sheath.
 8. The device of claim 1 whereinthe multi-layer, peelable sheath comprises a thermally stable outerlayer and at least one inner layer.
 9. The device of claim 8 wherein theinner layer comprises a detectable material capable of externalvisualization.
 10. The device of claim 8 wherein the thermally stableouter layer of the peelable sheath comprises a pigment.
 11. The deviceof claim 10 wherein the outer layer and inner layer of the peelablesheath each comprise visibly distinct pigments.